This invention relates to an improved process for recovery of petroleum from a geological formation containing it. In a particular aspect, this invention relates to an improvement in the process for improving petroleum production by the water-flooding process.
The yield of petroleum from a geological formation is usually far from the total petroleum present because once the pressure on the formation is relieved (or natural flow ceases) there is no easy method for recovering the residual petroleum. This residual petroleum tends to remain in the formation for a variety of reasons and flows to the producing well at a very slow rate--if at all.
It is known to improve petroleum recovery from a geological formation containing it by the process of water flooding. In this process, one or more wells spaced from the production well are drilled and water under pressure is pumped through these auxiliary wells into the surrounding formation. Ideally, the advancing water front sweeps residual petroleum before it to the production well where both water and petroleum are recovered. Actually, however, considerable petroleum is left behind in the formation and there have been numerous attempts to improve the recovery of this petroleum.
H. Atkinson, U.S. Pat. No. 1,651,311 and other workers proposed to improve petroleum recovery from a geological formation containing it by flooding the formation with water containing sodium hydroxide. Although several mechanisms have been proposed, the principal one is that the sodium hydroxide neutralizes organic acids present as components of the petroleum. The soaps thereby formed are surface active and help emulsify the petroleum thus promoting its removal from the formation. It was later discovered that emulsified oil could be substituted for the alkaline water and improve petroleum recovery. However, experience with these processes in the field has been disappointing in that yields did not improve to the extent that laboratory results would indicate. Many of the problems involved in the caustic water flooding process are discussed by H. Y. Jennings, Jr., et al., J. Pet. Tech., December 1974, pages 1344-1352. Among other problems, the authors show that calcium in the water, as well as rock reactivity is deleterious. A review of the history of the caustic and emulsion methods has been provided by C. E. Johnson, Jr., Ibid, January 1976, pages 85-92.
As previously mentioned, the acidic components present in most petroleum sources will react with alkali metal hydroxides to form soaps. However, soluble calcium and magnesium compounds are usually present in the reservoir waters and these also react with the alkali hydroxide. This is disadvantageous because it reduces the amount of sodium hydroxide available to form the petroleum soaps, and also generates undesirable, water-insoluble compounds which may tend to plug the formation.
There is, therefore, a need for an improved process for recovering petroleum by water flooding operations.